The U.S. Department of Justice has listened again to a tape recording made at Kent State University on May 4, 1970, when Ohio National Guardsmen fired on anti-war protesters, killing four students and injuring nine. Citing “insurmountable legal and evidentiary barriers,” the department will not reopen its investigation into the tragedy that set off waves of demonstrations and hardened attitudes against the Vietnam War.

Technology available to analyze the recording, made by student Terry Strubbe from a dorm window, has improved greatly since 1974. A re-analysis was pushed by Alan Canfora, one of the wounded students and director of the Kent May 4 Center, his penchant for finding conspiracies well-known. It was Canfora who found a cassette copy of the Strubbe tape in a Yale University archive in 2007, the original tape apparently destroyed.

U.S. Rep. Dennis Kucinich also requested that the Justice Department take another look, after an independent analysis of the tape prepared for the Cleveland Plain Dealer deciphered what appears to be a male voice giving the command to prepare to fire. When experts at the FBI listened, they found the evidence inconclusive.

Justice officials remind that time and protections against double jeopardy prevent further action against the surviving guardsmen. Still, the historical record remains incomplete, especially on the issue of what caused the soldiers to shoot for 13 deadly seconds. Were they following orders when they fired into a crowd of unarmed students?

The true value of pursuing an independent, expert analysis of the Strubbe tape, as requested by Canfora, is that modern technology, able to filter noise and enhance sounds, could provide the answer to that lingering question, filling in a crucial part of the historical record. Besides the possible command to fire, the independent experts hired by the Plain Dealer also reported sounds of shots from a .38-caliber pistol some 70 seconds before the guardsmen fired.

As the May 4 story slips into history, the ranks of those who observed what happened grows thinner and thinner. Perhaps the Strubbe tape will provide the crucial link to those past events. The possibility is enough for the Justice Department to go forward with an independent evaluation.